Astronomy C

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Unome
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Re: Astronomy C

Postby Unome » April 2nd, 2018, 2:08 pm

AlphaTauri wrote:I also wrote this test! (syo also helped with this one.)

I think I made it a bit too difficult for a Regionals... again. Sorry.

Scored 71-74 depending on credit for ambiguous answers. This test was significantly harder than MIT.

How does #73 work? I came up with all sorts of nonsensical answers but couldn't figure out what to do to combine the orbits.

Also what's going on with #35? Pretty sure those are supernovae spectra
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Re: Astronomy C

Postby AlphaTauri » April 2nd, 2018, 5:02 pm

Unome wrote:Scored 71-74 depending on credit for ambiguous answers. This test was significantly harder than MIT.

Not every invite has to be impossible, you know :P (Honestly, I think Tad/Donna do a much better job of difficulty than I do.)

How does #73 work? I came up with all sorts of nonsensical answers but couldn't figure out what to do to combine the orbits.

Find the radii of both orbits around the center of mass via (I should have specified circular orbits), and average them to get half the major axis.

Also what's going on with #35? Pretty sure those are supernovae spectra

I derped and put the wrong image on the image sheet. ("Oh right, the spectra question. Must be this picture, right?") I'll upload a fixed version...

Edit: Fixed.
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Re: Astronomy C

Postby Unome » April 2nd, 2018, 5:08 pm

AlphaTauri wrote:
Unome wrote:Scored 71-74 depending on credit for ambiguous answers. This test was significantly harder than MIT.

Not every invite has to be impossible, you know :P (Honestly, I think Tad/Donna do a much better job of difficulty than I do.)

Agreed, but we also didn't need ~15% of the teams over 80%.

AlphaTauri wrote:
How does #73 work? I came up with all sorts of nonsensical answers but couldn't figure out what to do to combine the orbits.

Find the radii of both orbits around the center of mass via (I should have specified circular orbits), and average them to get half the major axis.

Oh I forgot to half it... ;-; rip 6 points
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Re: Astronomy C

Postby Magikarpmaster629 » April 2nd, 2018, 6:04 pm

AlphaTauri wrote:
Unome wrote:Scored 71-74 depending on credit for ambiguous answers. This test was significantly harder than MIT.

Not every invite has to be impossible, you know :P (Honestly, I think Tad/Donna do a much better job of difficulty than I do.)

Tbh your tests are the best, period (including nats) (well besides maybe nats 2016 that one was really good) (but other than that I've learned way more from yours than any others).
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Re: Astronomy C

Postby Unome » April 2nd, 2018, 7:18 pm

Magikarpmaster629 wrote:
AlphaTauri wrote:
Unome wrote:Scored 71-74 depending on credit for ambiguous answers. This test was significantly harder than MIT.

Not every invite has to be impossible, you know :P (Honestly, I think Tad/Donna do a much better job of difficulty than I do.)

Tbh your tests are the best, period (including nats) (well besides maybe nats 2016 that one was really good) (but other than that I've learned way more from yours than any others).

Hm, I thought the Nationals and MIT tests were of slightly better quality, but also generally easier than this one. The use of images and interpretation that they build into their math is probably part of it - although, can't really go hard on math for a regional. On this one it did seem like there was almost nothing between questions 51-70 below mid-difficulty though.
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Re: Astronomy C

Postby sciolyPA » April 3rd, 2018, 1:23 pm

Does anyone have the period-luminosity relationship for type II cepheids? I can only find type I.

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Re: Astronomy C

Postby Unome » April 3rd, 2018, 1:29 pm

sciolyPA wrote:Does anyone have the period-luminosity relationship for type II cepheids? I can only find type I.

Generally I just use a Type I relationship and add another 1.6 to the absolute magnitude.
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Re: Astronomy C

Postby Ten086 » April 5th, 2018, 9:30 pm

AlphaTauri wrote:
Unome wrote:Scored 71-74 depending on credit for ambiguous answers. This test was significantly harder than MIT.

Not every invite has to be impossible, you know :P (Honestly, I think Tad/Donna do a much better job of difficulty than I do.)

How does #73 work? I came up with all sorts of nonsensical answers but couldn't figure out what to do to combine the orbits.

Find the radii of both orbits around the center of mass via (I should have specified circular orbits), and average them to get half the major axis.

Also what's going on with #35? Pretty sure those are supernovae spectra

I derped and put the wrong image on the image sheet. ("Oh right, the spectra question. Must be this picture, right?") I'll upload a fixed version...

Edit: Fixed.


LOL so I took this with my partner for practice--when we started the test, you hadn't uploaded the fixed version yet, so I was pretty confused on those questions. Later in the test I accidentally closed the window and had to reopen it, and didn't notice that the image had changed. When we were going through our answers, I looked at that question again and was so shook because the image was different, and I thought I was out of my mind because I had no idea what I'd been looking at before--then I saw the forums today :')

I thought it was a rly good test, I missed like everything because I'm bad (quote my partner: "how did you put neutron star for a question where the answer was rotational energy????") but it was really good practice, so thank you for posting it! :v
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Re: Astronomy C

Postby Unome » April 6th, 2018, 6:37 pm

Upon reading a few papers - higher metallicity implies a dimmer Cepheid than predicted by the Leavitt relationship? I notice that a higher metallicity corresponds with a lower distance modulus, but for some reason I'm having trouble interpreting the latter.
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Re: Astronomy C

Postby antoine_ego » April 6th, 2018, 7:02 pm

Unome wrote:Upon reading a few papers - higher metallicity implies a dimmer Cepheid than predicted by the Leavitt relationship? I notice that a higher metallicity corresponds with a lower distance modulus, but for some reason I'm having trouble interpreting the latter.


Distance modulus is defined as m-M=mu, where m is the apparent magnitude and M is the absolute. For a given m, having a lower distance modulus implies that M is greater than expected. This makes sense with the metallicity, since a Type II Cepheid is typically 1.6 magnitudes dimmer, and thus has a greater absolute magnitude (recall that the absolute magnitude increases, as luminosity decreases).
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Re: Astronomy C

Postby Unome » April 7th, 2018, 6:13 am

antoine_ego wrote:
Unome wrote:Upon reading a few papers - higher metallicity implies a dimmer Cepheid than predicted by the Leavitt relationship? I notice that a higher metallicity corresponds with a lower distance modulus, but for some reason I'm having trouble interpreting the latter.


Distance modulus is defined as m-M=mu, where m is the apparent magnitude and M is the absolute. For a given m, having a lower distance modulus implies that M is greater than expected. This makes sense with the metallicity, since a Type II Cepheid is typically 1.6 magnitudes dimmer, and thus has a greater absolute magnitude (recall that the absolute magnitude increases, as luminosity decreases).

Ah, forgot about Type II... thanks.
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Re: Astronomy C

Postby Ten086 » April 17th, 2018, 8:56 am

What is the Astro test at nationals usually like? Do they go crazy with scientific papers and obscure info or anything like that, or is it usually pretty reasonable?
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Re: Astronomy C

Postby jonboyage » April 17th, 2018, 11:24 am

Ten086 wrote:What is the Astro test at nationals usually like? Do they go crazy with scientific papers and obscure info or anything like that, or is it usually pretty reasonable?


As far as I know, they do a good job with making sure you get some free points balanced with some general math and a few tougher more specific questions. However, some of the others here may have more experience than me so I may only have been exposed to the fair tests. I'm still expecting a reasonably challenging test that will test your knowledge fairly.
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Re: Astronomy C

Postby Adi1008 » April 17th, 2018, 9:35 pm

Ten086 wrote:What is the Astro test at nationals usually like? Do they go crazy with scientific papers and obscure info or anything like that, or is it usually pretty reasonable?

In my (admittedly very limited experience) nationals tests don't cover any esoteric information about research papers. In my sophomore year, I made a huge deal out of reading research papers for nationals and I think what helped me was the concepts I learned from them, not the fact that they are research papers. Figures/charts from research papers tend to show up (at least in 2016) but the questions that accompany them can be answered without any knowledge of the research paper itself by applying concepts and thinking really hard.

I think a good way to think about the nationals test is as a harder MIT test in terms of preparing as they are written by the same group of people.
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Re: Astronomy C

Postby Alex-RCHS » April 18th, 2018, 3:45 pm

What values do you normally use for the Hubble Constant?
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